The EU24 Button Expansion Module can expand the Avaya 2420 Digital Telephone with 24 additional call appearance/feature buttons. This unit features a large display for button labels (no paper labels needed) and is ideal for use in coverage applications. Note: When any of the expansion modules are connected, you must connect an auxiliary power supply to the telephone. An1151B1 local power supply (material code: 175706) or an 1151B2 local power supply (material code: 177087) with Battery Holdover is recommended.